1. Field of the Invention
The present invention relates to a high frequency filter device and assembly of which a central frequency and a bandwidth are variable.
2. Description of the Related Art
Generally, a high frequency filter is manufactured in such a manner that tuning is performed after fabrication and the resultant tuning configuration is fixed by an adhesive or the like, so that the filter's performance is not influenced environmental changes over time. Recently, a system using a plurality of bandwidths in a plurality of bands is demanded. To implement such a system, a filter bank is formed with a plurality of filters meeting respective requirements, that is, different center frequencies and different bandwidths. The signal paths are configured by a switch according to real-time requirements.
Here, if a frequency and a bandwidth of each filter can be varied as necessary, the filter bank, which is inefficient in terms of cost, space, and weight, may be replaced with a smaller number of filters.
Korean Patent Laid-open No. 10-2003-0009976 discloses a structure varying a central frequency and a bandwidth of a filter in a wide band using a varicap diode so that not only a resonant frequency of a resonator but also a coupling coefficient between resonators may be controlled. However, this is control of frequency-tuning elements by an electrical method. In general, electrically-tunable filters show very large insertion loss compared with mechanically-tunable filter.